Newsletter #35: morning or night measurements, cross-training
An important questions that has yet to be answered
hi there 👋
I hope everything is well. This week I have a few things I’d like to discuss.
First, measurement timing. I recently shared some of my data showing very good agreement between morning and night measurements (you can see it here). I have done this also in the past, as it seems that in my case, these measurements capture very similar responses.
There are of course differences, typically due to stressors timing and how night data tends to be tightly coupled with whatever you did in the evening, see for example the blog below where I discuss a simple example with late meals and irrelevant night HRV suppressions.
Following up on my data, Andrew Flatt showed how in his experience night data hardly ever changes, while morning data is a better representation of his stress response:
I have been thinking more about this response and the data I have seen from others too.
In particular, there are some obvious differences in relation to stressor timing and most importantly body position, which I cover in the blog below:
Published literature looking at these differences reports (full paper here):
“It could be argued that the morning .. being further away from previous stressors and closer to the following, would provide more relevant information on the current state of homeostasis”
“Furthermore, it can be speculated that nocturnal recordings would rather reflect the physiological and psychological load of the previous day than the actual state of recovery and readiness to perform on the following day”
These are important aspects, as the data is used in similar ways, but it does not necessarily capture the same processes.
However, this is not really what Andrew is saying. He mentions quite a different behavior of the data depending on when it is captured, to the point that night data seems less sensitive to stressors.
I have seen this in other cases over the year, and despite my own experience showing a very good agreement between these two measurements, I understand Andrew’s view and would argue that apart from the differences in the context of stressor timing and body position, measurement timing and the amount of data used (i.e. a full night versus a single spot check in the morning, following best practices) might result in the following:
night data: an overall health marker, more stable over time (outside of very large stressors such as sickness or excessive alcohol intake), and somewhat less responsive to acute physical and psychological stressors.
morning data: a more responsive indicator of acute and chronic stressors, especially when taken while sitting or standing up (orthostatic stressor). Possibly less coupled to overall health when taken in isolation.
I am curious to see if over the next years we will be able to better tease out important differences in these protocols, so that we can eventually use the most effective method based on our application of interest and physiology, more than the most heavily marketed :)
Stay tuned for updates.
Training talk: cross-training
This one is slightly off-topic but I figured it could be interesting to some.
In the past 6 weeks, I’ve mostly trained on the bike, while recovering from a running injury. It has been an interesting experiment.
Below I cover goals, expectations, changes in physiology, and learnings. I hope there is something useful for you too
Thank you for reading, and keep training.
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see you next week!
Marco holds a PhD cum laude in applied machine learning, a M.Sc. cum laude in computer science engineering, and a M.Sc. cum laude in human movement sciences and high-performance coaching.
He has published more than 50 papers and patents at the intersection between physiology, health, technology, and human performance.
He is co-founder of HRV4Training, advisor at Oura, guest lecturer at VU Amsterdam, and editor for IEEE Pervasive Computing Magazine. He loves running.
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Twitter: @altini_marco.
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